So I think you can consider the different cases as mentioned above.
So if you have N,O --> you have N, N, S, S, E, E left. You can arrange this in (6! / [2! * 2! * 2!]) because of the repeated letters.
If you have N,E --> you have O, N, S, E, N, S left. You can arrange this in (6! / [2! * 2!])
If you have S,O --> you have N, N, E, N, S, E left. You can arrange this in (6! / [3! * 2!])
If you have S,E --> you have N, O, N, S, E, N left. You can arrange this in (6! / 3!)